Antarctica Under Siege by Hidden Forces

Antarctica is losing more ice than ever, scientists reported in
2015. Its ice shelves — the thick, floating slabs that encircle the
continent — are taking the biggest hit. The shelves slow and
stabilize the glaciers behind them, but they are succumbing to a hidden
force: Deep, warming ocean currents are melting the ice from beneath.

The collapse of several small ice shelves has caused glaciers to
accelerate two- to ninefold and spill more ice into the ocean, raising
the sea level. A study published in April shows that more ice shelves are
coming into play: From 1994 to 2012, the rate of ice shelf shrinkage
increased twelvefold. Parts of the ice sheet considered at risk hold
enough ice to raise the global sea level by 22 feet. Here’s how our
understanding of Antarctica’s vulnerability advanced in 2015.

More Snow (But Less Ice)

Climatologists speculated in the 1990s
that Antarctica might actually slow the rate
of global sea level rise. They expected that
rising temperatures would produce more water
vapor, leading to more snowfall and more ice.
Researchers reported in March that over the
past 20,000 years, warmer temperatures have
indeed correlated with higher snowfall: For
each Fahrenheit degree of warming, snowfall
increased by about 2.7 percent. But that hasn’t
translated into a reversal of Antarctica’s ice loss.

Larsen B’s
Last Gasp

Glaciologists
reported in June
that the last
remnant of the
Larsen B Ice Shelf
is splintering,
and glaciers
flowing into it
are accelerating.
Its approaching
demise continues
a disturbing trend:
the progressive
collapse of
five ice shelves since 1989.

Next Up: Larsen C

The neighboring Larsen
C Ice Shelf could soon
enter the early stages of
collapse. A major crack is
advancing rapidly, reaching
an unprecedented 60 miles long in early 2015.

Southern Peninsula
Starts to Sweat

While the glaciers in this region seemed
stable, it turns out warming ocean
currents have been melting the underside
of the ice. Results published in May show
this region crossed an invisible threshold
in 2009, with a dozen major glaciers
simultaneously starting to thin, sweating
off 60 billion tons of ice per year.

Weak
Underbelly

The Amundsen
Sea coast is
the vulnerable
underbelly of
West Antarctica.
Its glaciers slide
on beds that lie
nearly a mile
below sea level,
exposing them to
ocean currents.
New data show
ice shelves are
collectively losing
100 billion tons
of ice per year,
and glaciers have
accelerated by up
to 70 percent.

Hidden Hazards in the East

East Antarctica, situated on high ground that
protects it from warming ocean currents, was
considered stable. But not exactly, according to
surveys with ice-penetrating radar. A March study
shows that one large swath of the ice sheet sits
on beds as deep as 8,000 feet below sea level and
is connected to warming ocean currents. Totten
Glacier, one of East Antarctica’s largest ocean
outlets, is already thinning — an ominous sign,
since this single glacier drains enough ice to raise
the sea level more than all of West Antarctica’s ice
loss would.

[This article originally appeared in print as "Antarctica Under Siege."]